In order to obtain depth information of an object to be examined, what is referred to as tomography was developed as far back as the 1960s. Tomographs are images free from overlays of all object details lying in a particular slice. With a tomograph an x-ray source is moved in a first plane from a point “A” to a point “B”, e.g. above the object to be examined, while an x-ray detector is moved below the object to be examined, for example in a plane parallel to the first plane, from point “B” to point “A”. As a result of the movements the projections of all points of the irradiated object move in the image plane. Sharp images are only obtained of those object areas of which the projections are moving in the film plane at the same speed as the x-ray detector. The first solutions for tomography possessed a “tomo bar” with which a mechanical coupling between x-ray source and x-ray detector was achieved, modern solutions possess an electronic control which controls the motorized drive for x-ray source and x-ray detector.
Tomo synthesis represents a further development of tomography. In this system the images are not simply averaged during the movement but are recorded individually and then fed to a 3D reconstruction method. The advantage is that not only one individual slice but a number of parallel slices can be reconstructed. In addition the x-ray source can be moved in different scanning paths, such as ellipses, loops or spirals for example, with the scanning path always remaining in one plane however. A tomosynthesis system with a C-arm is known for example from DE 10 2007 037 996 A1.
3D x-ray imaging with this type of tomosynthesis system with a C-arm or with x-ray source and x-ray detector arranged mechanically independently of each other is far slower for example than computed tomography since a CT gantry can be rotated very quickly because of its mechanical properties.